In traditional switch mode power supply (SMPS) for supplying a bus voltage VBS to a downstream device, such as a DC/DC converter for supplying a solid state drive (SSD) device, a high-voltage capacitor rated for a relatively high voltage (e.g., higher than 10V) is generally used as a storage capacitor to store energy when a power source is provided to the SMPS and to release the stored energy when a predetermined condition is satisfied, for example, when the bus voltage VBS drops below a release threshold, for power backup. In such a configuration using a high-voltage capacitor as the storage capacitor, a boost control scheme is generally used to step up the power source VIN to a higher storage voltage VSTRG across the high-voltage capacitor (e.g., VIN=3.3V, VSTRG=20V), and a buck control scheme is generally used to step down the storage voltage VSTRG across the high-voltage capacitor to the lower bus voltage VBS to supply the downstream device (e.g., VSTRG=20V, VBS=3.3V).
As another type of capacitors, low-voltage capacitors, e.g., super capacitors, get more and more attention nowadays due to their variety of advantages, such as their excellent reliability performance, low cost, quick charge/discharge capability, etc. However, compared with the high-voltage capacitor, the low-voltage capacitor has a lower rated voltage (e.g., several volts for a single low-voltage capacitor), which requires that the power source VIN is stepped down to a lower storage voltage VSTRG for the purpose of safe operation of the low-voltage capacitor (e.g., VIN=12V, VSTRG=5V). Accordingly, when used to supply the downstream device, the lower storage voltage VSTRG is stepped up to the higher bus voltage VBS (e.g., VSTRG=5V, VBS=12V). As a result, the traditional control scheme for the configuration using the high-voltage capacitor as the storage capacitor is no longer applicable for the low-voltage configuration using a low-voltage capacitor as the storage capacitor.
Depending on different situations, the user may choose high-voltage capacitor or low-voltage capacitor as the storage capacitor. Thus, there is a need for a SMPS capable of being used for both high-voltage capacitor and low-voltage capacitor. And the SMPS in accordance with the present invention addresses at least the above-mentioned issue.